Reducing and non reducing sugars

ESTIMATION OF REDUCING AND NON- REDUCING SUGARS IN JAGGERY OR SUGARCANE JUICE

Aim:

         To estimate the contents of reducing and non- reducing sugars in the given sample of Jaggery or sugarcane juice.

Principle:

         The reducing sugars contain an aldehyde or ketone group and therefore posses reducing properties. Hence they are estimated by titration with Fehling’s solution. The total reducing sugars are estimated by titration with Fehling’s solution after inversion of non- reducing sugars into reducing sugars using concentration hydrochloric acid. The percentage of non- reducing sugar is estimated by difference between the total reducing sugars and reducing sugars.

Reactions

1.     CHO                                                                        COOH

         (CHOH)4      +      2CuO                                   (CHOH)4               +         Cu2O

         CH2OH                                                                                CH2OH   

         Glucose               Copper oxide                      Gluconic acid          Cuprous

         (Reducing sugar)                                                                                           oxide 

2.  C12H22O11 +H2O                  C6H1206    +      C6H1206

      Sucrose                                                              Glucose                               Fructose

(non – reducing sugar)                                               (invert sugars)

Reagents:

i)        Lead acetate

ii)  Sodium oxalate

iii)    Fehling’s solution ‘A’- 69.28 g of pure copper sulphate in 1 lit water

iv)    Fehling’s solution ‘B’- 350 g of sodium potassium tartarate (Rochelle salt) and 100 g sodium hydroxide in 1 lit water

v)  Concentrated hydrochloric acid

vi) 40% sodium hydroxide

vii)  Phenolphthalein indicator

    viii) Methylene blue indicator

Procedure:

Clarification

         Weigh 20 g of jaggery and transfer to a 400 ml beaker. Add about 100 ml of water to dissolve it. Transfer to a 250 ml volumetric flask. Add one gram of solid lead acetate, shake well and make up to volume. Filter through No.3 fluted filter paper. To the filtrate add one gram of sodium oxalate and filter again through No 3 fluted filter paper. The filtrate obtained is the clarified jaggery solution.

Estimation of reducing sugars

·         Pipette out 5 ml of Fehling’s  A and 5 ml of Fehling’s B solution into 250 ml conical flask.

·         Add 40 ml of distilled water and 2-3 glass beads.

·         Boil the contents vigorously and titrate against the clarified jaggery solution or sugarcane juice until the blue colour just disappears and a light green colour is obtained.

·         Add 2-3 drops of methylene blue indicator and continue the titration till a brick red colour is obtained.

·         Record the total volume of jaggery solution consumed. Repeat the experiment with 5 ml of Fehling’s A and 5 ml of Fehling’s B and add the clarified jaggery solution 2 ml less of the previous value.

·         Boil the contents well and add 2-3 drops of methylene blue indicator. Titrate with jaggery solution till a brick red  colour is obtained.

Estimation of total reducing sugars

·         Pipette out 25 ml of the clarified jaggery or sugarcane juice solution into a 250 ml volumetric flask and add 10 ml of concentrated hydrochloric acid and keep it on a water bath for 8 minutes.

·         Cool the flask under tap water and neutralize the acidity with 40% sodium hydroxide using phenolphthalein as indicator.

·         Make up the volume to 250 ml and estimate the reducing sugars ‘as given above.

Observations and calculations

Weight of jaggery or sugarcane juice taken 

=

20 g

Volume of clarified jaggery solution prepared

=

250 ml       

Volume of jaggery solution used for the titration of reducing sugar

=

‘A’

10 ml of Fehling’s A ns B solution will reduce

=

0.05 g of glucose

If ‘A’ ml of jaggery solution 

=

0.05 g of glucose

250 ml  contains

=

0.05 X 250

 A

This is present in 20 grams of jiggery

Percentage of reducing sugars in jaggery

=

0.05 X 250 X 100

  A         20

Total reducing sugar              

Volume of clarified jaggery solution pipetted out for inversion

=

25 ml

Volume made up after inversion

=

250 ml

Volume of inverted sugar solution consumed during titration

=

‘B’ ml

10 ml of Fehling’s A and B solution will reduce

=

0.05 g of glucose

If ‘ B’ ml of inverted sugars solution will contain

=

0.05 g of glucose

250 ml of inverted sugar solution contain

=

0.05 X  250 

   B

250 ml of clarified jaggery solution contains

=

0.05 X 250 X 250

   B              25

This is present in 20 g of jaggery

Percentage of total reducing sugars

=

0.05 X 250 X  250 X100

   B               25   X  20

Result

         The amount of non- reducing sugars expressed in terms of sucrose i.e., total reducing sugars – reducing sugar x 0.95.